1. Field of the Invention
This invention is in the field of heat treatment of finely divided materials such as pulverized raw material to be used in the manufacture of cement. It involves the use of two rows of cyclone separators arranged in series with a calcination furnace being connected to one of the rows and a material cooler being connected to the other of the rows. Significant increases in efficiency of heat utilization are achieved by controlling the parameters of operation in the rows of cyclone separators and the distribution of material therebetween.
2. Description of the Prior Art
In the case of previously conventional methods for the production of cement clinkers from pulverized raw material to be used in the manufacture of cement, the pulverized raw material is preheated in suspension type gas heat exchangers resulting in very little calcination. The preheated raw materials were subsequently conveyed into a rotary kiln for sintering but only about half of the rotary kiln would be used for sintering since one half had to be used for the calcining of the pulverized raw material. These installations were reasonably economical for average output yields up to approximately 2000 metric tons per day with respect to the distribution of the heat load between the suspension gas heat exchangers and the sintering furnace.
The trend to higher output yields had to be followed by improvements in conventional heat exchangers whereby the calcination of the pulverized raw material took place in the heat exchanger with the aid of a separate calcining device so that in the rotary kiln, only the sintering of the pulverized raw material would be undertaken and an appreciable thermal load was removed from the rotary kiln. In this manner, the output yields of the new installations could be increased without substantial enlargement of the dimensions or of the investment cost for the rotary kiln. With this development the suspension gas heater-rotary kiln system, it was possible to redesign or convert existing installations with only average outputs to installations with a high output yield.
In German Laid Open Specification No. 22 62 213 there is described a system combining a cyclone heat exchanger with a rotary kiln wherein the output was increased by adding an additional cyclone heat exchanger which acted on the exhaust air of the clinker cooler, so that in this heat exchanger the endothermic process of the complete calcination of the pulverized raw material to be used in the manufacture of cement took place. Both heat exchangers consisted in a series of four cyclone steps. The raw material which was delivered into the heat exchanger which acted on exhaust gases of the rotary kiln, after passing through the heat exchanger were subsequently conveyed to the heat exchanger which acted on the cooler exhaust air. The entire quantity of pulverized raw material of both heat exchangers, before the lowermost step of the heat exchanger acted on with the cooler exhaust air, was subjected to complete pre-calcination with an additional heat treatment.
In the case of this type of installation, however, the pre-calcination of the pulverized raw material is only obtained under unfavorable conditions, since with the same number of heat exchanger steps in the two parallel connected heat exchangers, the heat exchanger which is acted on by the hot air of the clinker-cooler and is provided with a calcination device must be driven with appreciably higher exhaust gas losses than the other which is acted on by the exhaust gases of the furnace. This increased loss of exhaust gas cannot be equalized by directing a higher quantity of pulverized raw material to the heat exchanger acted on by the cooler exhaust air.